Sunday 20 October 2019

optics - How does a holographic object change perspective when the image is rotated?


Fundamentally I want to know: How do holograms work?


The problem with that question is that normally you will end up with pages and pages talking about:



  • a laser

  • a beam splitter

  • a diffuser


  • the object being imaged

  • object beam

  • reference beam

  • mirror

  • holographic emulsion


Even Wikipedia is heavy on how to make a hologram, rather than how does a hologram work.




Other people have mentioned stereoscopic vision; how having two eyes gives the illusion of a 3d object. That is also irrelavent, since someone with one eye (or, in my case, one eye closed) can still experience a hologram.


What I am trying to figure out is how does a hologram work?. More to the point, how is it that rotating a flat holographic sticker allows the virtual object to change orientation - allowing me to see content that was not there a moment ago?





Wikipedia has an image that mentions reconstructing a virtual 3d object:


enter image description here


Some problems that that image, though, is that my credit card:



  • has no reference beam

  • is not being viewed at a 45 degree angle (meaning no interference can happen)


Assuming I have a holographic image of a simple cube. If I am looking at the holographic plate straight on, I will only see a square (i.e. the face of the cube closest to me):


enter image description here



If i rotate the holographic plate, so the right side of the plate is further away, the virtual cube will rotate, and I will actually be able to see the left face of the cube:


enter image description here


What is happening in the flat, 2-dimensional, holographic sticker that it can display continuously different information as I rotate it?


What is the mechanics of this holographic "paper" that it can present my eye different images?




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